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In recent months, Robin Dunbar, a professor of evolutionary psychology at Oxford university, has been inflicting pain on volunteers as part of an experiment in cognitive development. These pain tests come with a twist. Some of the volunteers have suffered their ordeals before and after watching golf videos or a serious theatre play (Dunbar travelled to the Edinburgh Fringe festival for a number of experiments). Others have watched comedy shows.

Dunbar’s exercise is producing a powerful insight: if you want to minimise pain, watch something funny, not golf videos. Better still, do it as part of a group of four people, since this typically increases laughter levels by up to 30 times. “The National Health Service could cut its costs dramatically just by doing this,” Dunbar observes, arguing that similar pain-reducing results can also be achieved by getting groups of people to dance together or perform religious rituals.

This should come as no surprise: we all instinctively know that dancing, laughing or going to jolly parties tends to put us in a better mood. But Dunbar thinks there is a more important evolutionary twist at work. Two decades ago, he shot to fame by declaring that the optimum size of a social group was about 150-strong; our human brains are simply not large enough to cope with the cognitive stress and complexities of maintaining close social ties with more people. Thus, if you look at the size of medieval European villages or how the Romans organised their armies – or even how many Christmas cards people typically send – that 150 number keeps cropping up. Primates, however, instinctively huddle in much smaller groups than humans because their brains are smaller.

When his thesis was made public, it caused a stir, particularly in tech circles. When I travelled to the Facebook campus in San Francisco a couple of years ago, for example, I discovered that the engineers there were obsessed with that “Dunbar number”, not just because it potentially influenced the size of online friendship groups but also because it shaped how Facebook organised its staff. When Facebook managers realised that their team of engineers was exceeding that magic 150 threshold, some six years ago, they deliberately introduced policies and rituals to keep the company “bonded”.

What fascinates Dunbar today is not simply that magic 150 number, but the question of how humans have evolved to enable this optimum group to bond. As he explains in a new book, Human Evolution, primates typically do this through “grooming” (ie combing each other for nits). This puts them in such close proximity to each other that it releases endorphins, creating a feel-good sense of social cohesion. But this is so time-consuming that “if we humans bonded with grooming we would need 45 per cent of our time”, Dunbar observes. “Instead, we typically spend just 20 per cent of our time on social interaction.”

Dunbar believes that humans have evolved to create more efficient ways of bonding, such as dancing, storytelling and shared laughter. These activities, like grooming, also release endorphins, which create a sense of group cohesion. And, as a byproduct, such endorphins reduce experienced pain. Thus humans have “evolved” to use laughter, dance, religion and storytelling to meet social and physiological needs.

In a country such as the US, where many people are uneasy about the whole concept of “evolution”, the idea of seeing cherished cultural rituals as merely endorphin-creating adaptive traits might seem offensive. Indeed, during most of the 20th century, academics who studied physical anthropology (ie human evolution) didn’t tend to analyse culture as well (even though Victorian anthropologists did study both 150 years ago). But Dunbar is one of a growing band of so-called evolutionary psychologists who are starting to take this blended approach.

If nothing else, their work raises some curious questions about not just the past but also our modern world. These days humans are increasingly communicating not through shared face-to-face rituals but electronic devices. Friendships are maintained by Facebook circles and emails, not trance dances. But can these new forms of communication release the same endorphin buzz as other, older rituals? And if children and teens try to “grow up” socially with their mobile phones, will they still be able to interact?

Some observers think so. As I wrote a few months ago, anthropologists such as Danah Boyd think that teenagers are forging new ways of roaming and bonding online. Dunbar, however, is more wary: he believes that humans need to meet face to face to maintain friendships; simply chatting on Facebook doesn’t work.

The one thing that is clear is that this debate is likely to intensify as online connectivity increases. And that is worth pondering if you start laughing with friends this weekend, either online or face to face. Instead of just being a way of passing the time, this is actually a crucial evolutionary mechanism that humans have developed to survive. Perhaps it is appropriate, then, that one of the most popular text messages is “LOL” (laugh out loud).